The present high intensity ink formulation is directed to printing in color. More particularly, the present high intensity ink formulation is directed to improved inks and a method for using the same to more accurately reproduce the colors of a subject in print media.
The printing industry attempts to reproduce images, pictures, and letters on a substrate to represent, as closely as possible, the colors of the original subject, whether the source of that subject is presented in a photograph, transparency, drawing, or painting. Unfortunately, the colors as viewed on a computer screen or a camera often are not what is finally printed on paper. For example, colors appear different on uncoated, coated, or matte stock paper. Similarly, the color on a digital screen may appear different than the color as it prints from, for example, an ink-jet printer on to paper. This is due to different color models being used to reproduce color in different media. A color model describes the way in which primary or base colors can be added or subtracted to form a variety of different colors. Examples of color models are the RGB color model and the CYMK color model.
Each color model has an associated color space chart in which the various colored areas (“color spaces”) that form the chart are the variations in color produced through mixing of the base or primary colors in the associated color model. The color space chart produced for each color model is made from a balance of inks with specific hues, at specific densities, at specific gain in dot values.
The process of creating a picture or photograph on print media first starts with a digital RGB model file from an electronic device, for example, a camera. RGB refers to red, green, and blue, the three hues of light that can be mixed to form the different color spaces in the RGB color space chart. The RGB model is commonly used in televisions, computer monitors, and computerized technology such as digital cameras.
A printer, however, uses a different color model, the CYMK color model. The CYMK model has base or primary colors of cyan, yellow, magenta, and black, which are used to create color images on a physical substrate such as paper, rather than red, green, and blue. Thus, to convert a digital image to a physical print image, the camera file, that is in terms of the RGB model, is converted to a CYMK model file, a file extension associated with raw cyan, magenta, yellow, and black samples. This CMYK file is then used to produce a color space chart file for printing the subject.
To reproduce a digital picture in physical print, a digital file of an image/picture is generated from a digital scanner or camera. This file is stored in the form of a Tiff, Jpeg or a RAW. A new color space pallet is generated on a printing press and the printing inks generally fall into a specific tolerance. The new color space is then scanned and manipulated to a specific tolerance and placed into a CMYK file. A color proof is then generated of the subjects through the manipulated color space file on a jet printer. The CMYK file is then used to generate four printing plates. The plates are put on a printing press and the inks used must have the same specifications as the one used to generate the color space chart. The printing press is, typically, set up to print specific color densities, at a specific dot gain value, in order to match the color proof.
Unfortunately, because of the different base or primary colors in each of the models, the shades and hues of similar colors may be subtly different in each color chart. For example, an apple may appear brighter or be slightly more orange in the RGB model than in the CMYK model or as compared to real life. This is due to the electronic medium imposing its own color palette and criteria for representation of the subject's colors that may not be compatible, acceptable, or appropriate for the printer in order to adequately or correctly reproduce the subject in physical print.
The printing industry has criteria that are used to determine the how accurately a color in one medium represents a subject of another medium. The printing industry uses “CIELAB” (also CIE L*A*B*) to determine the accuracy or perceptual continuity of the reproduced colors. CIELAB is a “perceptual color fidelity” metric, measuring how accurately the reproduction of a color is to the original subject when viewed by a human observer. It assigns a numerical value to a color to achieve balanced tones and match colors of a given picture.
CIELAB (also CIE L*A*B*) classifies color spaces by, among other things, associating tristimulus values with each color. A tristimulus value of a color is the amount of the three base/primary colors in a three-component additive color model needed to match a particular test color. An advantage to the CIELAB technique is that all color values can be calculated from the tristimulus values.
Another advantage of using CIELAB measurements is that it has the ability to compare color to color by their differences. Differences can be measured for a control color and a trial color. The distance between the two sets of color coordinates in a given three dimensional color space chart represents the color difference.
In printing, the ink film and density are controlled so as to allow for the optimum perceptual continuity or accuracy of reproduction. Color discrimination is also determined by the thickness and density of the ink applied to the substrate. Ink is measured on a printing press by a metric value based on mils (millimeters) (1 mil= 1/1000 of an inch or 0.001 inch). The thickness of the ink film on the printing press rollers is a guide to establish all of the mechanical functions of a printing ink. The ink film determines the strength, cure rate, rub resistance, and the dot structure on a substrate. The majority of printing inks are setup to print within the range of 0.20 mil to 0.50 mil. When inks fall within this range, the print characteristic are within the tolerance of acceptable performance. The following Table 1 lists the general performance characteristics of differing thicknesses of ink:
TABLE 1Type ofThickness of InkInk PrintedCharacteristics.20-.30 milLight ink filmSharp dots reproduction; may havecontrol and rub-resistance issues.30-.40 milMediumProduces acceptableink filmSWOP(standard web offset printing)dot reproduction: acceptable set andrub-resistance.40-.50 milHigh ink filmAcceptable color; generallyunacceptable dot reproduction andpotential to smear/dry improperly
The densitometer assigns numbers to density variations by quantifying the amount of light that is reflected from the surface of the color being measured. The densitometer gives a numerical reference to the amount of reflected light. For example, a reading of 0.00 indicates that 100% of the light has been reflected by the sample color. A reading of 1.00 indicates that 10% of the light is reflected. A reading of 2.00 indicates that only 1% of the light has been reflected. The logarithmic differences measured are important in determining the amount of color needed to develop a balanced picture on a printing press.
Dot value is also used as a measurement for color. For example a dot value of 50% refers to a measured color space of a color chart, wherein 50% of that space is color and 50% is white, an enlarged example of which is illustrated in FIG. 1.
The following TABLE 2 illustrates the densitometer readings for various thicknesses of ink, using Process Magenta, as the ink.
TABLE 2% Gain inrepresentation ofDensitometer ReadingThickness of ink in milscolor1.30-1.40.20-.2510%1.40-1.50.26-.3115%1.50-1.60.32-.3720%1.60-1.70.38-.4330%1.70-1.80.44-.4940%1.80-1.90.50-.5550%
Table 2 illustrates that the thicker the ink, the more accurately the ink represents the true or original subject color. An illustration of an example is in FIGS. 2A and 2B, where the dot value for both FIGS. 2A and 2B is 50%, but the thickness of the ink in FIG. 2B is thicker than FIG. 2A, and is perceived as more intense. However, when the ink thickness is increased, the mechanics and measurements, such as visual perception, ink mileage/consumption, set rub, and the like of the printing ink change exponentially.
Currently, in order to increase the visual perception of accurate representation of a printed picture using current ink and print technology, an increase in ink film thickness and density are required. This involves, however, running current print and ink technology out of currently acceptable standards, and negatively impacting the set rate, rub resistance, and dot structure of the ink.
Accordingly, there is a need to increase the color density or intensity of a printing ink, while maintaining its physical properties. The new color density, desirably, is perceived with greater ease than current color densities, and does not compromise the dot structure, rub resistance, smear resistance, or increase consumption of ink.